1. Field of the Invention
The present invention is applied to a gas engine provided with a spark plug; thereby, fuel gas is supplied to a pre-combustion chamber through a fuel gas inlet passage and the fuel gas supplied in the pre-combustion chamber is ignited by the spark discharge at the spark plug that is fitted on a seat surface in a mounting hardware piece for housing the spark plug.
2. Background of the Invention
FIG. 4 shows a cross-section around a pre-combustion chamber 4 of a conventional gas engine provided with a spark plug, the cross-section including the vertical center axis of the pre-combustion chamber.
In FIG. 4, a pre-combustion chamber mouthpiece 2 is fastened to and on the bottom wall of a cylinder head 1, the pre-combustion chamber mouthpiece being surrounded by a water chamber 1a; and, a pre-combustion chamber 4 is formed inside the pre-combustion chamber mouthpiece.
A mounting hardware piece 13 for housing the spark plug 13 thrusts the pre-combustion chamber mouthpiece 2 toward the bottom wall of the cylinder head 1; thus, the pre-combustion chamber mouthpiece 2 is fixed in the cylinder head.
The spark plug 10 (which vertical center axis is shown with the line 10a in FIG. 4) is fitted on the mounting hardware piece 13 via a fitting seat surface 50 and a gasket 10f, the spark plug being thrust toward the fitting seat surface 50 and the gasket 10f. 
Into the pre-combustion chamber, a fuel gas (for the pre-combustion in the pre-combustion chamber) is supplied through a solenoid controlled valve 23 for controlling the fuel gas supply, for example, by opening and closing the fuel gas passage in the solenoid valve, as well as through a fuel inlet passage 14; on a part way of the fuel inlet passage 14, a check valve 51 is provided, the valve 51 being a unidirectional valve which automatically opens with forward flow and closes against reverse flow. While the check valve is being opened, the fuel gas streams into the pre-combustion chamber 4 (which vertical center axis is shown with the line 4a in FIG. 4) through a fuel gas inlet slot 5; the fuel gas having streamed into the chamber 4 is ignited by the spark discharge at the spark plug; thus, flames and combustion gas is generated in the pre-combustion chamber 4.
Further, the flames and combustion gas generated in the pre-combustion chamber 4 gush into the main combustion chamber 60 through at least one torch jet nozzle 3 provided at the lower part of the pre-combustion chamber mouthpiece; the flames and combustion gas gushing into the main combustion chamber 60 ignite the lean, prefixed air-fuel mixture that is induced into the main chamber 60 through the intake air passages (not shown); and, the lean, premixed air-fuel mixture burns in the main chamber 60.
In the fuel inlet passage of the conventional gas engine provided with the spark plug 10 as described above, the check valve 51 that streams only forward flow; the pressures of high temperature conditions in the pre-combustion chamber 4 work on the check valve 51, from below upward; on the other hand, the fuel gas supplied in the pre-combustion chamber 4 is often difficult, to burn completely; the imperfect combustion causes soot, and the soot generated in the pre-combustion chamber 4 tends to be collected around the check valve 51 or the seat of the valve. The soot deposit often causes the adhesion of the check valve toward the fitting component thereof or the adhesion of the seat thereof; and, the soot deposit often causes the poor condition of the seat surface between the check valve and the bearing component thereof.
The patent reference 1 (JP2000-8960) discloses a pre-combustion chamber fuel gas supply device in which fuel gas is supplied to the pre-combustion chamber from a fuel gas reforming apparatus (that is provided with a solenoid valve at the gas discharge side of the apparatus), through a check valve that is arranged just above the pre-combustion chamber, the check valve being a unidirectional valve which automatically opens with forward flow and closes against reverse flow.
The patent reference 2 (JP1996-240152) discloses a pre-combustion chamber fuel gas supply device in which a bail valve type check valve and a needle valve type check valve are arranged in series in the fuel inlet type so that the carbon adhesion of the check valves is prevented, the adhesion being caused by excessively high temperatures.
In a case of a gas engine provided with a spark plug 10 as shown in FIG. 4, the check valve 51 is arranged just above the pre-combustion chamber 4; thus, as described above, the pressures of high temperature conditions in the pre-combustion chamber 4 work on the check valve 51, from below upward; the fuel gas supplied in the pre-combustion chamber 4 is often difficult to burn completely; the imperfect combustion causes soot, and the soot generated in the pre-combustion chamber 4 tends to be collected around the check valve 51 or the seat of the valve. The soot deposit often causes the adhesion of the check valve toward the fitting component thereof or the adhesion of the seat thereof; further, the soot tends to cause the adhesion of the solenoid valve or the deterioration of the poor seat conditions as to the check valve and the solenoid valve. Hence, it becomes necessary to restrain the temperature rise of the check valve 51 and the neighborhood thereof.
The fuel gas is supplied to the check valve 51 through the solenoid valve 23 for controlling the fuel gas supply and the fuel inlet passage 14; as described above, in a case where a difficulty of the check valve 51 is caused, for example, by the soot generation, it becomes also difficult to prevent the solenoid valve 23 from causing a malfunction, as is pointed out in the patent reference 1 (JP2000-8960).
Further, it is required to pay attention to the loss due to the dead volume in the fuel inlet passage; hereby, the dead volume means unnecessary space to supply the fuel gas of the prescribed fuel flow rate, into the pre-combustion chamber.
However, the patent reference 2 (JP1996-240152) only discloses the approach by which a bail valve type check valve and a needle valve type check valve are arranged in series in the fuel inlet type.